In a typical refrigeration system, refrigerant (in a vapor state) is compressed by a compressor unit driven by a motor. The compressed refrigerant, at high temperature and pressure, enters the condenser where heat is removed from the compressed refrigerant and the refrigerant changes to a liquid state. The refrigerant then travels through a filter dryer to an expansion device. The expansion device throttles the refrigerant as the refrigerant flows through an orifice, which causes the refrigerant to change phase from liquid to a saturated liquid/vapor mixture. The mixture then enters an evaporator, where heat is drawn from the environment to replace the latent heat of vaporization of the refrigerant, thus cooling the environmental air and causing the refrigerant to change to a vapor state. The low pressure refrigerant flow from the evaporator returns to the suction side of the compressor to begin the cycle anew.
To operate the system as a heat pump, a reversing valve can be provided and the flow is diverted such that the original evaporator becomes the condenser, the original condenser becomes the evaporator and the flow through the liquid line reverses. Heat is then drawn from a heat sink, and provided to the environment to heat the environmental air.
Filter dryers are well-known in this field and utilize a filter dryer medium and simple interconnections with the plumbing of the system to separate particles and remove water contaminants from the refrigerant in the system.
One particularly useful filter dryer is shown in Grahl, et al., U.S. Pat. No. 4,255,940, which is owned by the assignee of the present invention. In the Grahl dryer, loose molecular sieve material is enclosed within a tubular housing having an inlet port and an outlet port. The molecular sieve is retained at one end of the housing by a cup-shaped filter basket formed of a fine mesh screen. The basket is fixed in place near the outlet port of the housing by means of a double-folded marginal flange which engages the inner surface of the housing. The shape of the filter basket provides increased surface area for filtration as compared to, e.g., a flat filter screen. The molecular sieve is retained at the other end of the housing by a dual baffle assembly. The dual baffle assembly includes first and second perforated baffles, with the first baffle having a peripheral flange sized to fixedly engage the inner surface of the housing near the inlet port, and the second baffle being in direct contact with the molecular sieve material and having a peripheral flange sized to be in sliding relation with the housing. A compression spring is disposed between the first and second baffles to urge the second baffle against the molecular sieve material to maintain the molecular sieve material in a compacted state during use.
While the Grahl dryer has had success in the marketplace, it is intended primarily for unidirectional flow through the dryer, that is, flow from the inlet through the dual baffle arrangement, through the molecular sieve, and then through the screen basket to the outlet. The dryer is not intended to be connected within the refrigeration system for flow in the opposite direction, as the loose molecular sieve material can leak through and around the movable second baffle of the dual baffle arrangement, and then through the openings in the first baffle, and enter the downstream portion of the refrigeration system. It is therefore necessary to separately label the ports of the filter dryer for correct hook-up, and care must be taken during the plumbing of the system to confirm that the dryer is correctly oriented.
It can also be desirable in some applications to filter the refrigerant prior to the refrigerant entering the molecular sieve material. This can increase the useful life of the molecular sieve material.
Bi-directional filter dryers are also known, for example as shown in Griffin, U.S. Pat. No. 4,954,252, which is also owned by the assignee of the present invention. In the Griffin dryer, a valving structure includes a pair of identical check valve assemblies at either end of a molded desiccant core. Each check valve assembly includes reed-type flapper valves formed from a single sheet of material. The Griffin dryer is appropriate for many biflow applications, however, the dual check valve assemblies increase the material and assembly cost of the filter dryer, and the molded desiccant core is generally more expensive than loose molecular sieve material.
As such, while the known filter dryers may be appropriate for certain applications, applicants believe that there is a demand for a filter dryer for an air-conditioning system which uses loose molecular sieve material as a desiccant, and which can be connected in the system for refrigerant flow in either direction. It is therefore not necessary to separately label the ports of the filter dryer, or to have concern that the dryer could be connected in the wrong orientation. In addition, it is believed there is a continual demand for new and unique filter dryer which is economical, meets the performance and reliability demands in the industry, and which requires a minimum of components which are relatively easy and straight-forward to manufacture and assemble.